/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 29489
 * Date: 2023-03-01
 * Time: 22:29
 */
import java.util.Scanner;
public class Main2 {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNextLine())
        {
            String str = sc.nextLine();
            String s[] = str.split(" ");
            int sum = 0;
            for(int i = 1; i < s.length; i++)
            {
                int data = Integer.parseInt(s[i]);
                sum += data;
            }
            int ave = sum/(s.length-1);
            System.out.println(s[0]+":"+ave);
            //System.out.println(ave);
        }
    }
}
